When my kids grow a little and they are going to start using the Internet, I am going to be very clear about the rules in place for the use of the Internet. I am going to explain to them who those rules are and I am also going to tell them that those rules are non-negotiable. I am going to be as clear about them as possible.
I believe that it is a good idea to set some sort of punishment for not obeying the Internet rules. One idea that comes to my mind here right now is temporarily preventing my kids from using the Internet for a certain amount of time.